Cherry tree rootstock named ‘Cass’

ABSTRACT

A new cherry tree variety suitable for use as rootstock.

Botanical designation: The present invention relates to a new cherry tree variety. Based on a visual assessment of the seed parent, it appeared to be a natural species hybrid, of unknown complexity among three species within the Prunus subgenus CERASUS section Cerasus Koehne that are native to the collection region and cross naturally in the wild. These three species are Prunus avium L., Prunus cerasus L., and Prunus fruacosa Pall. The seed resulted from open-pollination and the paternal parent is unknown.

Variety denomination: The new plant has the varietal denomination ‘Cass’.

BACKGROUND OF THE INVENTION

This invention relates to a new and distinct variety cherry tree. In the field of plant genetics, researchers conduct an extensive and continuing plant-breeding program including the organization and asexual reproduction of orchard trees, and of which plums, peaches, nectarines, apricots, cherries, almonds and interspecifics are exemplary. It was against this background of activities that the present variety of cherry tree was originated and asexually reproduced in our experimental orchard.

PRIOR VARIETIES

Among the existing varieties of cherry trees, which are known to us, and mentioned herein ‘Hedelfingen’ (not patented); ‘Montmorency’ (not patented); ‘Bing’ (not patented); GI 148/2 cherry rootstock (U.S. Plant Pat. No. 9,644); and GI 148/1 cherry rootstalk (U.S. Plant Pat. No. 8,954).

ORIGIN OF THE VARIETY

Open-pollinated Prunus cherry seeds were collected in Pázmánd, Hungary, seeds were germinated at Michigan State University, East Lansing, Mich., and the resulting seedlings were planted in Clarksville, Mich. in 1998. Seedlings were selected as candidate rootstocks based on overall plant health, virus tolerance (Bromoviridae Ilarvirus species Prune Dwarf Virus and Bromoviridae Ilarvirus species Prunus Necrotic Ringspot Virus), and rooting percentage of softwood cuttings. Candidate rootstocks produced by asexual propagation were grafted with ‘Hedelfingen’ scion and planted in Clarksville, Mich. Further rootstock selection occurred on the basis of scion qualities to include precocity (early flowering and fruiting beginning the second year after planting) and reduced tree stature measured as trunk cross-sectional area. ‘Cass’ was asexually reproduced through conventional softwood cutting methods, and grafted with ‘Bing’ scion. The ‘Bing’ trees grafted on the ‘Cass’ rootstock were planted in Prosser, Wash. and evaluated for scion trunk cross-sectional area, tree height, growth habit, flowers per node, crop yield, cropping efficiency, and fruit weight, among other traits. Cherry tree ‘Cass’ was selected from this trial.

ASEXUAL REPRODUCTION OF VARIETY

Asexual reproduction of the ‘Cass’ cherry rootstock was achieved using the mother plant to obtain rooted liners using conventional softwood cutting procedures, and through meristem culture with commercial nurseries. Initially, liners were propagated from softwood cuttings in commercial greenhouses. A subset of these liners was used to establish a mother block in Clarksville, Mich. The remaining liners were sent to a nursery to make test trees of ‘Cass’ that were budded with the scion ‘Hedefingen’. The resulting trees were planted in a trial in Clarksville, Mich. A second set of liners was propagated from softwood cuttings in commercial greenhouses. These ‘Cass’ liners were budded with ‘Bing’ scion to make trees for a trial in Prosser, Wash. A nursery established meristem cultures of ‘Cass’, and using the plantlets produced they increased the liner number of ‘Cass’. These liners were used to make trees with ‘Montmorency’ scion for a trial in Traverse City, Mich. The living tissues (i.e. leaves, stems, buds, flowers and fruits) of the original mother block plants were observed to be identical to secondary and tertiary vegetatively propagated plants.

STATEMENT OF STABILITY

Asexual propagation as described has demonstrated that the combination of traits that characterize this tree are fixed and remain true to type through at least two successive propagation cycles.

SUMMARY OF THE INVENTION

‘Cass’ is particularly useful as a rootstock. The variety results in dwarf trees with significantly smaller canopy size than traditional non-dwarfing rootstocks. When this variety is used as a rootstock for sweet cherry, the fruit can be harvested without using ladders. When used as a rootstock for sour cherry the fruit can be harvested by an over the row harvester that can move continuously down the row instead of being harvested by a trunk shaking machine that harvests each tree individually. The variety of the invention also has favorable precocity, which results in a scion variety having flower buds and fruit beginning in years two and three rather than years five or six when traditional rootstocks are used. ‘Cass’ was selected as a cherry rootstock on the basis of its scion's trunk cross-sectional area (TCSA), tree height, growth habit, flowers per node, crop yield, cropping efficiency, and fruit weight, among other traits, in two experimental field trials. Scion trees grafted onto this rootstock showed significant reduction in TCSA. ‘Cass’ is suitable for standard nursery propagation practices for uniform liner production. ‘Cass’ can be distinguished from its parents and siblings by the use of Simple Sequence Repeat DNA markers. With primer pair PceGA59, ‘Cass’ is distinguished by the absence of the 182, and 189 bp alleles and the presence of the 186, 194, and 226 alleles. With the primer pair PruG4RS, ‘Cass’ is distinguished by the presence of the 172 and 182 alleles and the absence of the 190, 192, 196, 198, and 200 bp alleles.

BRIEF DESCRIPTION OF PHOTOGRAPHS

The accompanying photographs display flowers, leaves, leaves image 2 and fruits from a self-rooted mother block tree at Clarksville, Mich., planted in 2005

FIG. 1 is a photograph of the flowers of CASS (May 2014);

FIG. 2 is a photograph of two leaves of CASS (July 2013);

FIG. 3 is a photograph of five leaves of CASS with a ruler to show size (July 2013);

FIG. 4 is a photograph of cherries from and a seed from CASS (July 2013);

FIG. 5 is a photograph of the young tree of CASS (July 2015);

FIG. 6 is a photograph of an older tree of CASS (2016);

DESCRIPTION OF THE NEW VARIETY

The following is a detailed botanical description of the new variety of cherry tree, its flowers, foliage and fruit, as based on observations of various aged specimens grown at Clarksville, Mich. with color in accordance with The Royal Horticultural Society Colour Chart (R.H.S.), 2001 edition.

-   Measurement details: -   Flowers: -   Inflorescence height: Measured from where the flower cluster     attaches to the branch to the most distal floral part. -   Flower diameter: Measured across the petals in mm. -   Flower length: Measured from the bottom of the pedicel to the most     distal flower point (mm). -   Pedicel: The stem of an individual flower. It is measured from the     attachment in the bud to the start of the perianth. -   Peduncle: A stalk supporting an inflorescence. In these selections,     the cherry flowers within a flower bud all start at the same base     and then the stalk separates into individual pedicels supporting     each flower. -   Anther color: Before the anther's dehisce, when they are still     bright yellow and plump. -   Anther length: Measured for the longest anther measured from the top     of the perianth tube. -   Style: Measured above the swelled ovary. -   Tree:     -   -   Height.—Approx. 8 ft.         -   Diameter.—Approx. 8 ft.         -   Vigor.—Weak.         -   Branching habit.—Spreading.         -   Branching.—Strong.         -   Hardiness.—Cold Tolerant.         -   Plant.—Flowers: present.         -   Scion compatibility confirmed.—Hedelfingen, Bing,             Montmorency. -   Stem (trunk):     -   -   Strength.—Weak.         -   Texture.—Rough.         -   Color.—Grey brown (RHS 200A). -   A comparison of the stems of ‘Cass’ and ‘GiSelA® 6’ (GI 148/1) is     provided in Table 1 below:

TABLE 1 Botanical GiSelA ® 6’ description ‘Cass’ (GI 148/1) Stem strength weak medium Stem texture rough rough Stem color grey brown grey brown

-   One year old shoot:     -   -   Thickness.—Thin         -   Length of internode (middle third of shoot—mean of 10).—1.5             cm (1.1-2.3).         -   Pubescence (upper third).—Absent.         -   Number of lenticels.—10.         -   Anthocyanin coloration of apex.—Absent.         -   Position of vegetative bud in relation to shoot.—Markedly             held out.         -   Shape of apex of vegetative bud.—Acute.         -   Branching.—Medium.         -   Feathering.—Weak. -   Leaves:     -   -   Mature leaf arrangement.—Alternate.         -   Intensity of anthocyanin coloration of young leaf (during             rapid growth).—Weak.         -   Leaf blade shape.—Elliptic.         -   Leaf blade.—Ratio length to width: 1.9.         -   Leaf length-blade only (cm).—5.7.         -   Leaf width (cm).—2.6.         -   Leaf blade angle of apex (excluding tip).—Right-angled.         -   Leaf blade shape of base.—Obtuse.         -   Leaf blade shape of apex (e.g., acute).—Right-angled.         -   Leaf blade.—Incisions of margin: crenate.         -   Leaf blade.—Depth of incisions of margin: shallow.         -   Leaf blade color of upper side.—Light green (RHS 137B).         -   Leaf blade glossiness of upper side.—Medium.         -   Leaf blade.—Pubescence of lower side of apex: weak.         -   Petiole.—Presence of pubescence of upper side: absent.         -   Petiole.—Intensity of pubescence of upper side: weak.         -   Petiole.—Depth of groove: medium.         -   Leaf ratio length of leaf blade/length of petiole.—6.4.         -   Leaf.—Presence of nectaries: present.         -   Varieties with nectaries only.—Leaf — predominant number of             nectaries: two.         -   Leaf.—Position of nectaries: base of leaf blade.         -   Nectary shape.—Round.         -   Upper surface color (R.H.S.).—137B.         -   Leaf upper surface texture/pubescence.—Smooth.         -   Leaf upper surface venation color (R.H.S.).—138A.         -   Lower surface color (R.H.S.).—137C.         -   Leaf lower surface texture/pubescence.—Weak pubescence.         -   Leaf lower surface venation color (R.H.S.).—138C.         -   Leaf stipule frequency.—Absent.         -   Leaf petiole length (mm).—8.         -   Leaf petiole diameter (mm).—1.         -   Leaf petiole color (R.H.S.).—138B. -   A comparison of the leaves of ‘Cass’ and ‘GiSelA® 6’ (GI 148/1) is     provided in Table 2 below:

TABLE 2 Botanical GiSelA ® 6’ description Cass (GI 148/1) Mature leaf alternate alternate arrangement Leaf length-blade 5.7 8.7 only (cm) Leaf width (cm) 2.6 5.4 Laminae apex right- acute angled Leaf upper surface smooth smooth texture/pubescence Leaf upper surface 138A 138A venation color (RHS) Leaf lower surface weak medium texture/pubescence pubescence pubescence Leaf lower surface 138C 138C venation color (RHS) Leaf stipule rare present frequency Leaf stipule length — 6 (mm) Leaf stipule width — 2 (mm) Leaf stipule shape — pointed Leaf stipule margin — serrated Leaf petiole length 8 11 (mm) Leaf petiole 1 1.6 diameter (mm) Leaf petiole color 138B 138B and 59A (RHS)

-   Flowers:     -   -   Flowers per cluster.—3 to 4.         -   Fragrance.—None.         -   Bloom date (50%).—May 8, 2016.         -   Inflorescence height (cm).—3.4.         -   Inflorescence diameter (cm).—2.7.         -   Flower diameter (mm).—16.         -   Flower length (mm).—25.         -   Petal number per flower.—5.         -   Petal arrangement.—Flat whorl.         -   Petal length (mm).—10.         -   Petal width (mm).—8.         -   Petal shape.—Oval.         -   Petal apex.—Round.         -   Petal margin.—Smooth.         -   Petal texture.—Smooth (both upper and lower sides).         -   Petal color when fully opened.—Upper surface (R.H.S.): 155D.         -   Petal color when fully opened.—Lower surface (R.H.S.): 155D.         -   Sepal number.—5.         -   Sepal length (mm).—3.5.         -   Sepal width (mm).—2.0.         -   Sepal shape.—Triangle.         -   Sepal apex.—Pointed.         -   Sepal margin.—Slightly serrated.         -   Sepal texture.—Smooth (both upper and lower sides).         -   Sepal color upper (R.H.S.).—138B.         -   Sepal color lower (R.H.S.).—138B with some 59A.         -   Flower pedicel length (mm).—20.         -   Flower pedicel diameter (mm).—1.         -   Flower pedicel angle (degrees).—20.         -   Flower pedicel texture.—Smooth.         -   Flower pedicel color (R.H.S.).—138B.         -   Flower peduncle length (mm).—4.         -   Flower peduncle diameter (mm).—2.         -   Flower peduncle texture.—Smooth.         -   Flower peduncle color.—138B.         -   Pistils.—Number per flower: 1.         -   Pistil length (mm).—12.         -   Pistil color (R.H.S.).—149B.         -   Style length (mm).—10.         -   Style color.—138C.         -   Stigma shape.—Round/indented.         -   Stigma color (R.H.S.).—138B.         -   Stamens.—Number per flower: 27.         -   Longest filament length (mm).—10.         -   Stamen filament color (R.H.S.).—155D.         -   Longest anther length (mm).—7.         -   Anther color (R.H.S.).—20B.         -   Pollen color (R.H.S.).—17C.         -   Pollen amount.—Moderate. -   A comparison of the flowers of ‘Cass’ and ‘GiSelA® 6’ (GI 148/1) is     provided in Table 3 below:

TABLE 3 GiSelA ® 6’ Botanical description ‘Cass’ (GI 148/1) Flower fragrance none none Entire flower bloom period — — Individual flower bloom — — period Inflorescence height (cm) 3.4 3.5 Inflorescence diameter (cm) 2.7 3/7 Flower diameter (mm) 16 24 Flower length (mm) 25 31 Petal arrangement flat whorl flat whorl Petal shape oval oval/round Petal apex Round Round Petal margin smooth smooth Petal texture smooth smooth Petal color - upper surface 155D 155D Petal color - lower surface 155D 155D Sepal shape triangle triangle Sepal apex pointed pointed Sepal margin slightly serrated serrated Sepal texture smooth smooth Sepal color (upper) 138B 138B Sepal color (lower) 138B with some 59A with some 59A 138B Flower pedicel length (mm) 20 15 Flower pedicel diameter 1 1 (mm) Flower pedicel angle 20 30 (degrees) Flower pedicel texture smooth smooth Flower pedicel color 138B 59A to 138B Flower peduncle length 4 8 (mm) Flower peduncle diameter 2 2 (mm) Flower peduncle texture smooth smooth Flower peduncle color 138B 138B Number of pistils per flower 1 1 Style length (mm) 10 8 Style color 138C 138C Stigma shape round/indented round/indented Stigma color 138B 138B Stamen filament color 155D 155D (RHS) Anther length (mm) 7 7 Anther color (RHS) 9B 9B Pollen color (RHS) 17C 17C

-   Fruit:     -   -   Mature fruit shape.—Flat-round.         -   Mature fruit height (mm).—14.1.         -   Mature fruit width 1 (mm).—14.0.         -   Mature fruit width 2 (mm).—15.6.         -   Mature fruit ratio height/width 2.—0.90.         -   Mature fruit weight (g).—2.2.         -   Mature fruit flesh taste.—Sour.         -   Mature fruit skin color (R.H.S.).—46A.         -   Mature fruit flesh color (R.H.S.).—23C.         -   Stone color (R.H.S.).—164D.         -   Stone shape.—Elongate.         -   Stone number.—1.         -   Stone height (mm).—10.8.         -   Stone width 1 (mm).—6.3.         -   Stone width 2 (mm).—5.1.         -   Stone ratio height/width 2.—2.11.         -   Stone weight (g).—0.15.         -   Fruit stem length (mm).—39. -   A comparison of the fruit of ‘Cass’ and ‘GiSelA® 6’ (GI 148/1) is     provided in Table 4 below:

TABLE 4 GiSelA ® 6’ Botanical description ‘Cass’ (GI 148/1) Mature fruit shape flat-round round Mature fruit flesh taste sour sweet-sour Mature fruit flesh color 23C 23C (RHS) Mature fruit skin color 46A 45A Stone color (RHS) 164D 164D Stone shape elongate oval Stone number 1 1

SIMPLE SEQUENCE REPEAT (SSR) MATERIALS AND METHODS

The use of clonally propagated Prunus sp. rootstocks in cherry production is increasing as these rootstocks provide reduced tree size and precocity. DNA markers that differentiate rootstocks are an important tool to verify identity among these rootstocks during the vegetative propagation stage. The simple sequence repeat (SSR) marker PceGA59 was previously determined to uniquely distinguish the commercially available GiSelA® (GI 148/2 and GI 148/1) rootstocks (Struss et al. 2002).

A targeted approach was used to develop a second SSR that was capable of providing differentiation of the rootstock selections of the invention and others by the inventors. The approach used was based on the ability to obtain genome-wide SNP (Single Nucleotide Polymorphism) data using the Illumina Infinium® cherry SNP array (Peace et al. 2012). An analysis of genome-wide SNP data for the rootstocks resulted in the identification of a genomic region on linkage group 4 that was likely to differ among the MSU rootstocks.

Using the peach genome sequence, an SSR marker was designed to target this region. This SSR marker, termed PruG4RS, successfully differentiated the MSU rootstocks. The development of PruG4RS and its combined use with PceGA59 has successfully circumvented the limitations of each individual marker and proven effective for use as a “quality control” DNA diagnostic tool for the commercial GiSelA® (GI 148/2 and GI 148/1) rootstocks as well as the MSU breeding program rootstock selections.

SSR Markers Used

Fingerprinting was performed using two simple sequence repeat (SSR) markers: PceGA59 and PruG4RS. The forward and reverse primers sequences for these two SSR markers are as follows:

TABLE 5 Primer name Primer sequence 5′ → 3′ PceGA59_redesigned_F TGAACCCCTCTACAAATTTTCC PceGA59_redesigned_R GACTGTAGAACCCAAAAGAACG PruG4RS-F TCAGAAAAGAAATTGCAACGGG PruG4RS-R CTT AGT GGT CTA GTC TGC ATG C

The first primer pair, PceGA59, was published in Struss et al. (2002). However, the primer sequence reflects the addition of GC clamps. Based on genetic data for the MSU cherry rootstocks we designed a second primer, PruG4RS (Andersen et al. 2015)

Plant Material Used and DNA Extraction

Cherry DNA was extracted from young unfolded leaf blades using the procedure of Edge-Garza et al. (2014).

Polymerase Chain Reaction (PCR)

PCR amplification was performed for the two SSRs using the following conditions: 94° C. for 5 min followed by 9 cycles of 94° C. for 30 s, 60° C. for 45 s (−1° C. per cycle), 72° C. for 1 min and then 24 cycles of 94° C. for 30 s, 55° C. for 45 s, 72° C. for 1 min with an elongation step of 72° C. for 5 min.

Gel Electrophoresis and Fragment Visualization

The PCR products were visualized by electrophoresis on a 6% denaturing polyacrylamide gel in a 50 cm Sequi-Gen GT vertical sequencing apparatus (Bio-Rad Laboratories, Hercules, Calif.) for 2.5 hours at 70 watts with 1× TBE buffer. Following electrophoresis, the gels were stained with the Silver Sequence DNA Sequencing System (Promega Corporation, Madison, Wis.) and dried for 24 hours. DNA fragment sizes were scored visually using 10 and 50 base pair ladders (Invitrogen Corporation, Carlsbad, Calif.).

TABLE 6 DNA Fingerprint Data PceGA59 Allele (bp) 182 186 189 194 226 Cass + + + ‘GiSelA ® 5’ + + + (GI 148/2) ‘GiSelA ® 6’ + + + (GI 148/1) PruG4RS Allele (bp) 172 182 190 192 196 198 200 Cass + + ‘GiSelA ® 5’ + + (GI 148/2) ‘GiSelA ® 6’ + + (GI 148/1)

All references cited herein, are hereby incorporated in their entirety by reference, including but not limited to the following which relate to determination of various alleles.

Struss D, Boritzki M, Karle R, and Iezzoni A F. 2002. Microsatellite markers differentiate eight Giessen cherry rootstocks. Hort Science 37: 191-193.

Andersen K, Sebolt A, Stegmeir T, Iezzoni A. 2015. Development of the Simple Sequence Repeat marker PruG4RS for the differentiation of cherry rootstocks. American Society for Horticultural Sciences Annual Conference, New Orleans, La., August 4-7, Poster #023.

Edge-Garza, D., Rowland, T., Haendiges, S. and Peace, C. 2014. A high-throughput and cost-efficient DNA extraction protocol for the tree fruit crops apple, sweet cherry, and peach relying on silica beads during tissue sampling. Molecular Breeding 34:2225-2228. 

I claim:
 1. A new and distinct variety of cherry tree substantially as described and illustrated herein. 